The Theoretical Approach And Experimental Study On The Structural Damage Assessment Based On Modal Analysis

In the fields of civil engineering, aerospace engineering and naval architecture, structural damages such as cracking, corroding and ageing etc. to some degree often occur during the structures'service life, on account of some elements such as use duration and design defect etc. Some invisible defections do not alert these structures in time and may result in major calamity accidents, causing plenty of loss of life and property to our country. Therefore, the research on damage identification has already becoming a mutually concerned issue in overseas and domestic academic field. Moreover, the method based on modal analysis has caused wide public concern because of its high efficiency and conveniences, becoming a hot topic in the domain of damage assessment.For the purpose to damage localization, the paper detects damages in a simply-supported beam according to certain damage evaluation indexes, and this study is in accordance with the theory of modal analysis, by the means of numerical simulation and test. The method is part of direct problem in dynamics. In this paper, we start the research from the curvature mode and residual force vector methods. According to numerical simulation with some degree of noise being added, these methods could achieve satisfactory effect using single order only when the modes measured in the test achieve a good accuracy. And this result is also confirmed in the test.Under the actual working condition, the noise could not be prevented happening in the test as a result of the site environment complexity. It usually performances that the relative error of certain order is too large, particularly when the damage positions are near the node of this mode, it is even improbable to detect the damage locations. Consequently, the paper presents the weighting mode displacement superposition method, based on structural modal analysis, in order to reduce the influence of the large-error mode. This method just needs the first five modes of structure which can be obtained simply in the test, and the concept of weighting coefficient is introduced which improves the capability of damage identification method. Numerical examples and experimental result show that the proposed method works well for the damage detection and the assessments are in good agreement with the actual condition. From the standpoint of modal analysis, this paper studies the weighting mode displacement superposition method, based on the traditional damage identification methods. The method shows high computational efficiency and reliability with a simple theoretical basis through approach of numerical simulation and experimental model. The results can be used as a theoretic and engineering guidance for the damage assessment.